Photoprinters or copiers, particularly of the diazo or white print variety, used for making copies of engineering drawings, are frequently rather wide in order to handle drawings of all sizes. Machines capable of handling drawings whose width is 36 inches or more are in common use. The exposure portion of such a machine frequently comprises a horizontal rotating illumination cylinder (which in some cases is itself a fluorescent lamp bulb) together with belt and roll means for guiding the sheets around the illumination cylinder in close contact therewith.
Because the machines are so wide, the roll means must be correspondingly long, and since the rolls are transversely loaded by the resilient belts which they drive, there is a very significant tendency for the rolls to bend or bow in response to such belt tension, which, if allowed to occur, would result in many problems. In particular the bowing of the rolls would impair the paper feeding properties such that the paper is not fed flat and becomes crinkled in the process. Belt tracking difficulties can also occur. In order to minimize such problems, it is customary to construct these rolls on a comparatively massive scale with materials, diameters and wall thicknesses sufficient to prevent any significant deflection. This type of construction accounts for a very significant portion of the weight and cost of the machine, and a significant improvement would be enjoyed if some way could be found to materially reduce the stiffness requirements and thus the weight and cost of these rolls.